Existing wireless systems are designed to meet certain operational requirements. Two such requirements are call-blocking and call dropping rates. Call blocking rates relate to the percentage of calls originating from wireless devices to a network base station that are blocked, i.e., not accepted, by the base station for any of several possible reasons, such as congestion at the base station. Call dropping rates relate to calls that are initially accepted but are later terminated not at the request of one of the parties to the call but because, for example, the quality of a signal carrying a call which may be voice or data becomes unacceptable.
It is believed that call dropping is more irritating to a wireless caller than a blocked call. That is, someone engaged in an accepted, then dropped, call is more upset when her call is dropped than when she has to wait until a call is finally accepted for connection after being blocked. For this reason, the call blocking rate is usually set higher than the call dropping rate. However, ideally, both call-blocking and call dropping rates should remain relatively low, e.g., ideally 1-2% and 0.1-0.2%, respectively. There is a tradeoff, however, between the two. Statistically, the higher the number of calls that are accepted, i.e., the lower the call blocking rate, the greater the chance that some calls will have to be subsequently dropped not at the request of a party, i.e., the higher the call dropping rate, and vice-versa.
For example, during certain times of the day a base station may experience a large influx of traffic, e.g., incoming telephone calls, that usually adds background interference to a wireless signal between a wireless device and its serving base station(s). This weakens the signal at a faster rate and results in a higher hand-off rate to another base station. In response to such an influx of traffic, (and/or to unrelated causes, such as user mobility patterns) the base station may attempt to hand-off some calls to neighboring base stations listed on a so-called neighbor list (a so-called “network assisted hand-off”) or an associated wireless device may attempt to originate a hand-off to another base station on the list (“mobile assisted hand-off”). The neighbor list contains a number of neighboring base stations that are ranked by one or more techniques known in the art. Typically, this ranking is based on a statistical model. The modeling and ranking are usually done when the base station or its associated network is initially deployed and is rarely revised. Typically, when the base station needs to hand-off a call, it first attempts to do so using a base station from the neighbor list that momentarily offers the best available wireless signal to a particular call, or simply by using the highest ranked base station on the neighbor list. Sometimes, however, such a hand-off is not possible because a connection to such a base station is momentarily unavailable (due to traffic congestion at the momentarily preferred base station) or the quality of the signal is unacceptable.
When this occurs, the base station will attempt to hand the call off to another base station on the neighbor list that momentarily offers the second best available wireless signal or simply to the next highest ranked base station. Sometimes, however, the base stations available to accept the hand-off are those that offer a weaker, but still acceptable, signal or those that are lower ranked base stations. Many times after a call is handed-off to such a base station the call is ultimately dropped because the base station that accepted the hand-off cannot maintain the call, e.g., it's too far away from the caller (or the signal drops under an acceptable threshold and cannot return to an acceptable level). In sum, though the signal between the lower ranked base station was momentarily acceptable, it quickly became unacceptable as the wireless user moved or as the traffic conditions associated with the base station changed. In hindsight, it would have been better, i.e., less irritating to block a number of incoming calls than to force a call to be handed-off to a less preferred, momentarily available base station and then be dropped.
Today, call blocking and call dropping rates are based on static neighbor lists, i.e., the lists remain relatively unchanged. This makes it difficult to change these rates as traffic conditions vary.